One time programmable (OTP) memory is a type of memory used within semiconductor integrated circuits (ICs) to program and permanently store information. OTP memory is often implemented with a fuse structure that relies upon the severing of a fuse link to store information. Once programmed, the OTP memory cannot be rewritten as programming entails breaking the fuse link. Fuses comprise a fuse link electrically coupling two separate electrical nodes, e.g., an anode and a cathode. Upon the application of a particular stressor to the fuse, the fuse link can be “broken.” The break in the fuse link creates an increase in the resistance of a conductive path, possibly an open circuit, between the two electrical nodes. Thus, the fuse has two different programmable states. The first programmable state exists when the fuse has a low resistance in the conductive path through the fuse prior to breaking the fuse link. The second programmable state exists when the fuse has a high resistance in the conductive path through the fuse subsequent to breaking the fuse link.
One type of fuse used to implement OTP memory is the electrically programmable fuse, which is often referred to as an e-fuse. To program an e-fuse, a voltage potential, with a constant polarity, is applied across a conductive fuse link via the cathode and the anode. The fuse link is typically formed of a silicided polysilicon layer overlaying a dielectric material. The applied voltage potential generates a current through the fuse link of sufficient magnitude to initiate electromigration in the silicided layer forming the fuse link.
Electromigration refers to the transportation of material by the gradual movement of ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. Electromigration is more significant in IC applications where higher direct current densities occur. Current traveling through the e-fuse generates electromigration effects that migrate material away from one or more portions of the cathode, anode, or fuse link regions. The migration results in a higher resistance in the conductive path through the e-fuse. Typically, a large current density is required to flow through the fuse link to induce electromigration within the e-fuse. To generate large current densities within an e-fuse, the application of significant programming voltages to the e-fuse may be necessary.